TN : TP ratio and planktivorous fish do not affect nutrient-chlorophyll relationships in shallow lakes

Authors: WANG, HAI-JUN; LIANG, XIAO-MIN; JIANG, PING-HONG; WANG, JIAN; WU, SHI-KAI; WANG, HONG-ZHU

Source: Freshwater Biology, Volume 53, Number 5, May 2008 , pp. 935-944(10)

Buy & download fulltext article:

Price: $48.00 plus tax (Refund Policy)

Abstract:

Summary

1. In previous work, phytoplankton regulation in freshwater lakes has been associated with many factors. Among these, the ratio of total nitrogen to total phosphorus (TN : TP) has been widely proposed as an index to identify whether phytoplankton are N- or P-limited. From another point of view, it has been suggested that planktivorous fish can be used to control phytoplankton.

2. Large-scale investigations of phytoplankton biomass [measured as chlorophyll a, (chl-a)] were carried out in 45 mid-lower Yangtze shallow lakes to test hypotheses concerning nutrient limitation (assessed with TN : TP ratios) and phytoplankton control by planktivorous fish.

3. Regression analyses indicated that TP was the primary regulating factor and TN the second regulating factor for both annual and summer phytoplankton chl-a. In separate nutrient-chl-a regression analyses for lakes of different TN : TP ratios, TP was also superior to TN in predicting chl-a at all particular TN : TP ranges and over the entire TN : TP spectrum. Further analyses found that chl-a : TP was not influenced by TN : TP, while chl-a : TN was positively and highly correlated to TP : TN.

4. Based on these results, and others in the literature, we argue that the TN : TP ratio is inappropriate as an index to identify limiting nutrients. It is almost impossible to specify a `cut-off' TN : TP ratio to identify a limiting nutrient for a multi-species community because optimal N : P ratios vary greatly among phytoplankton species.

5. Lakes with yields of planktivorous fish (silver and bighead carp, the species native to China) >100 kg ha⁻¹ had significantly higher chl-a and lower Secchi depth than those with yields <100 kg ha⁻¹. TP-chl-a and TP-Secchi depth relationships are not significantly different between lakes with yields >100 kg ha⁻¹ or <100 kg ha⁻¹. These results indicate that the fish failed to decrease chl-a yield or enhance Z_SD. Therefore, silver carp and bighead carp are not recommended as a biotic agent for phytoplankton control in lake management if the goal is to control the entire phytoplankton and to enhance water quality.

Keywords: chlorophyll-a; phytoplankton; planktivorous fish; total nitrogen : total phosphorus ratio; total phosphorus

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2427.2007.01950.x

Affiliations: 1: State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China

Publication date: 2008-05-01

TN : TP ratio and planktivorous fish do not affect nutrient-chlorophyll relationships in shallow lakes

Buy & download fulltext article:

Tools

Key

Text size:

Useful pages